import urllib, hashlib
from django import template

register = template.Library()

@register.simple_tag
def gravatar(email):
	"""
	Simply gets the Gravatar for the commenter.

	Template Syntax::

		{% gravatar comment.user_email %}
	"""

	url = "http://www.gravatar.com/avatar/"
	url += hashlib.md5(email).hexdigest()
	url += "?d=identicon&amp;s=40"

	return """<img src="%s" alt="" class="gravatar">""" % (url)


COMPARISON_DICT = {
		'less': lambda x: x < 0,
		'less_or_equal': lambda x: x <= 0,
		'greater_or_equal': lambda x: x >= 0,
		'greater': lambda x: x > 0,
		}


class ComparisonNode(template.Node):
	def __init__(self, var1, var2, comparison, nodelist_true, nodelist_false):
		self.var1 = template.Variable(var1)
		self.var2 = template.Variable(var2)
		self.comparison = comparison
		self.nodelist_true, self.nodelist_false = nodelist_true, nodelist_false

	def render(self, context):
		try:
			result = cmp(self.var1.resolve(context),
					self.var2.resolve(context))
			if COMPARISON_DICT[self.comparison](result):
				return self.nodelist_true.render(context)
		# If either variable fails to resolve, return nothing.
		except template.VariableDoesNotExist:
			return ''
		# If the types don't permit comparison, return nothing.
		except TypeError:
			return ''
		return self.nodelist_false.render(context)


def do_comparison(parser, token):
	"""
	Compares two values.

	Syntax::

		{% if_[comparison] [var1] [var2] %}
		...
		{% else %}
		...
		{% endif_[comparison] %}

	The {% else %} block is optional, and ``var1`` and ``var2`` may be
	variables or literal values.

	Supported comparisons are ``less``, ``less_or_equal``, ``greater``
	and ``greater_or_equal``.

	Examples::

		{% if_less some_object.id 3 %}
		<p>{{ some_object }} has an id less than 3.</p>
		{% endif_less %}

		{% if_greater_or_equal forloop.counter 4 %}
		<p>This is at least the fifth time through the loop.</p>
		{% else %}
		<p>This is one of the first four trips through the loop.</p>
		{% endif_greater_or_equal %}

	"""
	bits = token.contents.split()
	if len(bits) != 3:
		raise template.TemplateSyntaxError("'%s' tag takes two arguments" % bits[0])
	end_tag = 'end' + bits[0]
	nodelist_true = parser.parse(('else', end_tag))
	token = parser.next_token()
	if token.contents == 'else':
		nodelist_false = parser.parse((end_tag,))
		parser.delete_first_token()
	else:
		nodelist_false = template.NodeList()
	comparison = bits[0].split('if_')[1]
	return ComparisonNode(bits[1], bits[2], comparison, nodelist_true, nodelist_false)

for tag_name in ('if_less', 'if_less_or_equal', 'if_greater_or_equal', 'if_greater'):
	register.tag(tag_name, do_comparison)

